The electric pulse expansion of tubes is often carried out with the use of an electric fuse of the type that comprises a casing, a filler and an initiating wire. Such a fuse is inserted into a tube to be expanded. As the electrode approaches the electric fuse, an electric pulse is applied to the initiating wire, and a high-voltage explosion of that wire follows. The resultant shock wave acts through the filler upon the internal surface of the tube which is expanded because of the elastic-plastic deformation.
The aforedescribed process is used to expand tubes of heat exchangers with flat tube plates in which the tubes are arranged at specific distances from each other in horizontal rows. The number of distances between tubes in a row is equal to the number of tubes to be expanded. To expand tubes of such heat exchangers, the electrode has to be movable both in the vertical and horizontal planes.
Apart from expanding tubes of heat exchangers, expanders of the aforedescribed type can be used to expand tubes without tube plates, or tubes accommodated in a die. They may also be used to perform other operations in which deformation of tubes is involved.
A known electric tube expander (cf. USSR Inventor's Certificate No. 352,510, IPC B 21a, 26/10; B 21d, 39/06) comprises a bed with a vertical guide and horizontal guides thereon. An electrode is movably mounted on the vertical guide. Mounted on the horizontal guides are drives for moving the electrode in vertical and horizontal planes. The drives are provided with electrode distance of movement setting mechanisms. Each drive is a pneumatic cylinder incorporating pneumatic arresters which are actuated one after another during motion of the piston of the cylinder. The distance of movement setting mechanisms are adjustable stops installed in each pneumatic cylinder.
The known expander has the disadvantage of not being rapidly readjustable for different tube arragements. The pneumatic cylinders do not make it possible to accurately position the electrode in relation to the tube, so that part of the energy is wasted to span the gap between the electrode and the electric fuse lead.
Furthermore, it is difficult to adjust the electrode and control system of the known expander to the first tube of another row of tubes of a heat exchanger.